4.1 Program Objectives and Scope
- 4.1.1 Voluntary vs. Mandatory Risk Reduction
- 4.1.2 Performance-Based Design Concepts
- 4.1.3 Legal Considerations
Several recent earthquakes in the United States have provided evidence suggesting that nonstructural damage may account for more than 50% of total damage in future domestic earthquakes. As advances are made in the structural design of buildings, and we experience fewer structural failures and fewer collapses as a result, the significance of nonstructural damage becomes more apparent. In addition, postearthquake operations are of increasing concern not only to essential facilities such as police and fire stations and hospitals, but also to manufacturing facilities, banks, mobile phone providers, and many other businesses concerned with loss of revenue or loss of market share that would result from a lengthy outage following an earthquake. Organizations and owners who want to reduce their seismic exposure will need to address the nonstructural hazards in their facilities.
Seismic improvements to existing buildings might be mandated by a governmental body or might be motivated by a desire to provide for postearthquake operations, to reduce future losses or liability, to reduce insurance premiums, or to increase the resale value of the property. In most cases, seismic improvements to existing facilities are undertaken on a voluntary basis and, as a result, organizations and owners have latitude in setting the objectives and defining the scope of a nonstructural risk reduction program for existing buildings.
In general, a nonstructural risk reduction program for existing buildings would be considered a voluntary upgrade; that is, a program that is voluntarily undertaken by an owner to reduce the potential liability and losses in the event of an earthquake. Although current codes have requirements for bracing and anchorage of nonstructural items, most jurisdictions do not currently require nonstructural hazards to be addressed retroactively in existing facilities.
There are some notable exceptions, in cases where a jurisdiction may require mandatory retrofitting of existing nonstructural components. A few of these are listed below:
- Many jurisdictions in California have ordinances requiring that unreinforced masonry parapets, particularly those adjacent to a public right-of-way, be braced or anchored to prevent collapse in an earthquake.
- Some major cities including Chicago, New York, Boston, and Detroit have façade ordinances that mandate periodic inspection of building façades; while this is not intended as a seismic requirement, it has the benefit that the architectural cladding, veneer, ornamentation, and anchors are inspected and maintained on a regular basis.
- Seismic safety legislation (SB 1953) was passed in California in 1994, following the Northridge Earthquake. That earthquake resulted in the suspension of some or all services at 23 hospitals and in $3 billion in hospital-related damages. This legislation requires California hospitals to comply with specific nonstructural hazard mitigation deadlines, including: (1) major nonstructural items including emergency power supply, bulk medical gas systems, communication systems, fire alarm systems and exit lighting are to be braced by 2002; (2) most nonstructural items within "critical care areas" are to be braced by 2008; and (3) most nonstructural components within the hospital are to be braced by 2030. This is an unfunded mandate; the burden of financing these improvements rests with the health care providers.
- Major alterations, additions, or changes of use may trigger code requirements to bring existing construction, including the nonstructural items, into compliance with the current code. For instance, conversion of a warehouse to a school building would trigger requirements for current code compliance in many jurisdictions; check for local requirements and exemptions.
The rules that apply for voluntary upgrades to existing facilities are typically different than those that apply to new construction or to mandatory upgrades. While it may be desirable to design the nonstructural anchorage details for existing equipment in existing buildings using the current code, it is not typically required for voluntary upgrades. In order to describe the spectrum of risk reduction objectives, it is useful to introduce some performance-based design concepts.
The use of performance-based design concepts requires a discussion between building design professionals and their clients about performance expectations and seismic risk tolerance. Performance-based design provides terminology to characterize seismic risk and seismic performance and provides a framework for making comparisons between varying levels of seismic hazard, structural and nonstructural performance, postearthquake functionality, acceptable and unacceptable damage, and total earthquake losses over the expected life of the facility. Design professionals, organizational risk managers, building owners, business owners, and tenants all need to have an understanding of the tradeoffs between risk and reward; an understanding that seismic design and investment choices have a relationship to expected future performance and potential future losses. The parties all need to understand that they make choices, both passive and active, based on their understanding of the issues and their seismic risk tolerance. One may choose to live with known seismic risks or choose to initiate programs to reduce some or all of the known hazards; either way, a choice must be made.
General Interest Sidebar
Analogy: Financial Risk Tolerance
One of the first things most financial advisors do with new clients is to present them with an investment questionnaire to gauge how they feel about risking their money; that is, to assess what is referred to as their "investment risk tolerance." The investment advisor cannot make reasonable recommendations on how to allocate the client's assets without knowing something about their tolerance for financial risk. Is the investor conservative, moderate, or aggressive? Given the tradeoffs between risk and reward, do they have a low, medium, or high tolerance for financial risk?
Performance-based design concepts have been in development for several decades; this process is ongoing. These concepts are gradually finding their way into the building codes used for new construction, such as the International Building Code and Minimum Design Loads for Buildings and other Structures, and into the building standards used for the evaluation and retrofitting of existing structures, Seismic Evaluation of Existing Buildings (ASCE/SEI 31) and Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41), respectively. Previous editions of U.S. building codes were based on the philosophy that structures should not collapse in a major earthquake but might suffer severe structural and nonstructural damage; this was a minimum life safety standard and is roughly comparable to the Basic Safety Objective that is now described in ASCE/SEI 41-06. Although engineers were aware that a "code design" was only meeting minimum standards, it is not clear that building owners and occupants had a similar understanding. What is significant about performance-based design concepts is that they are used to describe a range of objectives and that they make the choice of performance objectives an explicit part of the design process; the design professional and the client need to discuss and agree on those performance objectives.
- Hazards Reduced—a postearthquake damage state in which nonstructural components are damaged and could potentially create falling hazards, but high hazard nonstructural components are secured to prevent falling into public assembly areas. Other life-safety issues, such as preservation of egress and protections of fire suppression systems are not addressed.
- Life Safety—a postearthquake damage state in which nonstructural components are damaged but the damage is not lifethreatening. However, significant and costly damage is expected to occur.
- Immediate Occupancy—a postearthquake damage state in which nonstructural components are damaged but building access and life-safety systems generally remain available and operable.
- Operational—a postearthquake state in which nonstructural components are able to support the pre-earthquake functions of the building.
While it is not relevant to describe the engineering design process of ASCE/SEI 41-06 in detail here, it is relevant to describe the decision making process used to determine the scope and desired performance objectives for a voluntary upgrade. Note that in addition to the Basic Safety Objective, the standard provides guidance on choosing objectives for voluntary upgrades that are both more ambitious, "Enhanced," and less ambitious, "Limited," than the Basic Safety Objective. The choice of objective will determine which hazards are addressed, what performance is likely following a major earthquake, and how much structural and nonstructural damage the facility is likely to sustain.
- What are the retrofitting objectives?
- What earthquake scenario(s) are most relevant for this facility?
- What kind of postearthquake functionality is required for this facility?
- What target structural performance level is required for this facility?
- What target nonstructural performance level is required for the facility?
- What target building performance level is required for the facility, and how does that relate to the target levels of structural and nonstructural performance and to the expected postearthquake damage state for the facility?
- What combination of choices meet the ASCE/SEI 41-06 Basic Safety Objectives? Enhanced Objectives? Limited Objectives?
|Target Building Performance Level||Expected Postearthquake Damage State||Target Structural Performance Level||Target Nonstructural Performance Level|
|Operational Level||Backup utility services maintain function; very little structural or nonstructural damage||Immediate Occupancy||Operational|
|The building remains safe to occupy; any structural or nonstructural repairs are minor||Immediate Occupancy||Immediate Occupancy|
|Intermediate Level||Damage Control|
|Life Safety||Structure remains stable and has significant reserve capacity; hazardous nonstructural damage is controlled||Life Safety||Life Safety|
|Intermediate Level||Limited Safety||Hazards Reduced|
|Collapse Prevention||The building remains standing, but only barely; the building may have severe structural and nonstructural damage||Collapse Prevention||Not Considered|
As shown in Table 4.1.2-1, buildings are assigned a target performance level, which considers both structural and nonstructural performance objectives.
In contrast to the approach used in ASCE/SEI 7-10 for new buildings where the nonstructural performance level is tied to a single ground shaking hazard, the nonstructural performance levels in ASCE/SEI 41-06 are defined in a manner independent of the ground motion. To establish criteria for a seismic retrofit, a ground shaking hazard level and corresponding structural and nonstructural performance levels are selected. Often, several sets of ground shaking hazards and nonstructural performance levels are established. For example, a building might have target building performance levels of Immediate Occupancy for thedesign earthquake ground motion and Life Safety for the maximum considered earthquake. Combinations of ground shaking hazard and performance level can be created to suit the needs and resources of the building owner. The engineering approach to nonstructural design ASCE/SEI 41-06 is discussed in Chapter 6 for different types of components.
According to ASCE/SEI 41-06, the Basic Safety Objective is achieved by the following combination:
- Design for Life Safety Building Performance for Basic Safety Earthquake 1 (earthquake that occurs every 500 years), AND
- Design for Collapse Prevention Building Performance for Basic Safety Earthquake 2 (earthquake that occurs every 2500 years).
All other combinations of performance levels and seismic hazard levels are characterized as either Limited or Enhanced objectives (for more on this, see sidebar below).
Limited and Enhanced Rehabilitation Objectives per ASCE/SEI 41-06
Besides the stated requirements for the Basic Safety Objective, all other combinations of performance levels and seismic hazard levels are characterized as either Enhanced or Limited objectives. In comparison with the Basic Safety Objective, a higher performance level correlates with less damage, lower losses, and increased functionality, whereas a lower performance level correlates with more damage, higher losses, and reduced functionality. The following are examples of Limited Rehabilitation Objectives:
- Address only serious nonstructural falling hazards considering a small, frequent seismic event, i.e., according to ASCE/SEI 41-06 terminology, target for a Hazards Reduced nonstructural performance level, considering the 50%/50 year event.
- Address all nonstructural life safety hazards without consideration of structural hazards, i.e., according to ASCE/SEI 41-06 terminology, target for a Life Safety nonstructural performance level for any chosen earthquake scenario.
In contrast, the following is an example for an Enhanced Rehabilitation Objective:
- Provide reduced damage and increased functionality, i.e., according to ASCE/SEI 41-06 terminology, design for Immediate Occupancy Building Performance for any earthquake hazard level. Note that to achieve this performance level, both structural and nonstructural upgrades may be required.
As seen in Table 4.1.2-1, an effort to preserve postearthquake operations at either the Immediate Occupancy level or the Operational levels require that both structural and nonstructural hazards be addressed. Indeed, the higher Operational standard for nonstructural components is what differentiates these two enhanced levels of building performance. Per ASCE/SEI 41-06, the differences in design between the different target levels of building performance are higher or lower seismic design forces and explicit design for more or fewer nonstructural components. Engineering analysis methods, such as nonlinear static and dynamic procedures, are available and can be used to check whether or not the design meets the target performance objectives. There are many other questions that may help refine the project objectives and scope of work, such as:
- What kind of losses can the business or organization tolerate after an earthquake?
- How much downtime can the organization tolerate before employees, clients, or customers go elsewhere?
- Does the organization have earthquake insurance? If so, how much of the losses are covered? What are the deductibles? What is the cost-benefit ratio of doing upgrades versus providing coverage and suffering a loss?
- Is this a historic building, essential facility, or facility with specialized or unique considerations?
- What nonstructural components are under your direct control? Architectural? Mechanical, electrical, and plumbing (MEP)? Furniture, fixtures, and equipment (FF&E)? Contents? Or all of these?
- Will the project include upgrades to only MEP and architectural components, or will FF&E and contents be included as well?
- What are the most hazardous nonstructural components?
- For leased facilities, which elements are responsibilities of the owner and which are responsibilities of the occupants?
- If the owner has undertaken any seismic upgrades, is there a report available describing the project objectives or design level? Were nonstructural items addressed?
- Are there any incentives a lessee can offer a building owner to improve the safety of leased space?
- Do you need to consider relocation to another space that provides an increased level of seismic safety?
ASCE/SEI 41-06 is in the last stages of an extensive revision. The new document, Seismic Evaluation and Retrofit of Existing Buildings (ASCE/SEI 41-13) merges ASCE/SEI 41-06 and Seismic Evaluation of Existing Buildings (ASCE/SEI 31-03). The nonstructural provisions of ASCE/SEI 41-13 will be significantly different than those found in ASCE/SEI 41-06. Major changes include:
- In most cases, the design ground motions for the performance objectives have been reduced. For example, in ASCE/SEI 41-06, the Basic Safety Objective was achieved by meeting LifeSafety structural performance criteria when subject to ground shaking having a 10% probability of exceedance in 50 years. In ASCE/SEI 41-13, Life Safety performance must be met for an earthquake having a 20% probability of exceedance in 50 years, a less severe event.
- The nonstructural performance objectives have been redefined.
- In ASCE/SEI 41-06, nonstructural performance objectives, from lowest to highest are: Hazards Reduced, Life Safety, Immediate Occupancy, and Operational. While the Operational performance objective is defined, the specific procedures and acceptance criteria were not provided.
- In ASCE/SEI 41-13, nonstructural performance objectives, from lowest to highest are: Life Safety, Position Retention, and Operational.
- There is no direct correlation between the old and new nonstructural performance objectives. Table 4.1.2-2 below illustrates the approximate relationship, but only in a general sense. There have been substantive changes to the nonstructural provisions throughout ASCE/SEI 41-13. Note the table is limited to performance objectives for which procedures and acceptance criteria are actually defined.
- To achieve the Basic Performance Objective in ASCE/SEI 41-13, nonstructural components in essential buildings (Seismic Risk Category IV), such as hospitals, emergency operations centers, and fire stations must meet the “Position Retention” objective—for roughly equivalent to “Life Safety” in ASCE/SEI 41-06. This represents a considerable reduction in requirements compared to the earlier edition.
|ASCE/SEI 41-06||ASCE/SEI 41-13|
|Hazards Reduced||Life Safety|
When FEMA E-74 is used in conjunction with ASCE/SEI 41-13, care must taken to properly determine the appropriate retrofit objective, design procedures, and acceptance criteria. This is of great importance since the term “Life Safety,” used throughout this document, has been redefined in ASCE/SEI-41-13 to mean a lower retrofit objective.
The point of including this discussion is not to discourage the reader by presenting the design process as a complex system, tempting the reader to conclude that it would be much easier to do nothing. The point of the discussion is to emphasize that choices need to be made in deciding how to manage seismic risk. Resources are always limited, and seismic risks must be balanced against many other types of risk. Whatever seismic hazard reduction objectives are selected, they should be chosen with an understanding of the risks and rewards. A decision to mitigate known seismic hazards, particularly dangerous life safety hazards, would generally be considered both reasonable and prudent, even if it were not mandated by law. A decision to upgrade a complex facility to Immediate Occupancy or Operational performance level is a major and complex undertaking, since facility operations may depend on the continued function of hundreds or thousands of individual nonstructural components. Such an upgrade should not be undertaken without an understanding of the costs and benefits of such a program.
A common concern voiced by building owners who are considering seismic improvement projects for their building or its nonstructural contents and components is the question of legal liability. A persistent belief is that one should not do anything, because if a life safety issue is uncovered and is made known to the owner, then the owner may be liable for any injuries or deaths that arise due to a severe earthquake damaging their building. This "ignorance is bliss" approach is not supported by legal precedents.
The legal issues involved are not black and white and may depend on the type of the facility, the sophistication of the owner, and the number of occupants at risk. There are two ways of looking at these issues:
- One view is that the standard of care of any owner is to act reasonably and to exercise ordinary care in managing the property. This care includes inspecting and maintaining owned buildings in a safe condition. Safety is usually measured against the building standard in effect at the time when the building was constructed, not the current code or any current evaluation standard for existing buildings. Therefore, if owners choose to evaluate their building using a more modern standard and uncover issues in doing so, it is then at their discretion on how, when, and if to act on these data in a voluntary manner.
- Another view is that if an owner is aware of a dangerous condition on their property, they have an affirmative duty to warn those affected or to mitigate the hazard.
If an owner does undertake a project or program to study and possibly to improve the seismic performance of a building or a building's nonstructural components, then the following is recommended to provide transparency:
- Ensure that any inspection is conducted by competent, qualified, and experienced parties
- Use widely accepted inspection, design, and construction standards such as those from FEMA, ASCE or other national or internationally recognized standard organizations
- Develop clear and complete documentation of decisions and actions
- Establish processes to ensure that all work is performed properly
- Implement any remedial actions through experienced contractors
- Proceed without creating any dangerous conditions and without making the building performance worse than it was before
- Proceed in a reasonable and responsible manner
The position of the authors is that an owner is much better off being proactive and doing something to investigate or improve the performance of a building and its nonstructural components and contents than doing nothing. Ultimately, however, an owner's decision to undertake such a remediation project is his or hers alone, and many considerations, such as public relations, risk tolerance, affordability, and market conditions will undoubtedly be factored into the decision.
It is recommended that an owner concerned with these issues seek appropriate legal counsel with expertise in construction law and seismic mitigation issues, to assist in their decision making process.